The present invention relates to a method of producing a semiconductor device, particularly, to a method of selectively forming a metal film on the surface of a semiconductor layer by a selective vapor growth technique.
Polycrystalline silicon (polysilicon) is widely used as the material of the gate electrode and interconnection electrode of a MOS type integrated circuit. However, polysilicon, even if doped with an impurity such as phosphorus, has a resistivity 100 times or more as high as that of a metal such as Al, with the result that a further improvement in the operation speed of an integrated circuit is obstructed by the use of polysilicon. Also, the recent miniaturization of the element is accompanied by a decrease in the junction depth, leading to a high resistance of the diffusion layer such as the source or drain region. The high operation speed of the integrated circuit is also obstructed by the high resistance of the diffusion layer mentioned above.
Recently, it is attempted to selectively form a metal film having a low resistivity on an electrode formed of polysilicon or on a semiconductor layer doped with an impurity, e.g. on a diffusion layer, by means of a vapor growth method. For example, a tungsten (W) film is selectively formed on a silicon or polysilicon layer by a vapor growth method using tungsten hexafluoride as the feed gas.
However, where a W layer is selectively grown on a diffusion layer formed in the surface region of a silicon substrate using, for example, an oxide film as a mask, a remarkable leak current takes place in the pn junction between the diffusion layer and the substrate, leading in some cases to a short circuiting. The deterioration of the junction property is rendered more serious as the junction depth is decreased. Thus, it is difficult to apply the above-noted method to a diffusion layer having a junction depth of 0.2 .mu.m or less.